Binary Star Imaging to Revolutionize Exoplanet Hunt?

Sept. 19, 2011 -- They're alien worlds orbiting distant stars far out of reach of detailed imaging by even our most advanced telescopes. And yet, day after day, we see vivid imaginings of these extrasolar planets with the help of the most talented space artists.
The definition of an extrasolar planet -- or "exoplanet" -- is simply a planetary body orbiting a star beyond our solar system, and nearly 700 of these extrasolar worlds have been discovered so far (plus hundreds more "candidate" worlds).
With the help of NASA's Kepler space telescope, the ESO's High Accuracy Radial velocity Planet Searcher (HARPS), French COROT space telescope and various other advanced exoplanet-hunting observatories, we are getting very good at detecting these worlds, but to glean some of the detail, we depend on artist's interpretations of fuzzy astronomical images and spectral analyses. That's the way it will be until we build a vast telescope that can directly image an exoplanet's atmosphere or physically travel to an alien star system.
So, with the flurry of recent exoplanet discoveries, Discovery News has collected a few of the dazzling pieces of art born from one of the most profound searches mankind has ever carried out: the search for alien worlds orbiting other stars; a journey that may ultimately turn up a true "Earth-like" world.

Image: Kepler-16b is the first exoplanet disc

View Caption+#2: The Transit

As an exoplanet passes in front of its star as viewed from Earth, a very slight dip in starlight brightness is detected. Observatories such as NASA's Kepler space telescope use this "transit method" to great effect, constantly detecting new worlds.

Image: An exoplanet passes in front of (or "t

View Caption+#3: Hot Jupiters

Some exoplanets orbit close to their parent stars. Due to their close proximity and generally large size, worlds known as "hot Jupiters" are easier to spot than their smaller, more distant-orbiting cousins.

Credit: ESO

View Caption+#4: Habitable Worlds

The primary thrust of exoplanet hunting is to find small, rocky worlds that orbit within their stars' "habitable zones." The habitable zone, also known as the "Goldilocks zone," is the region surrounding a star that is neither too hot nor too cold. At this sweet spot, liquid water may exist on the exoplanet's surface. Where there's water, there's the potential for life.

Image: An artist's impression of Gliese 581d,

View Caption+#5: A Phantom

Usually, exoplanet hunters look for the slight dimming of a star or a star's "wobble" to detect the presence of an exoplanet. However, in the case of Kepler-19c, its presence has been detected by analyzing its gravitational pull on another exoplanet, Kepler-19b.
Kepler-19c is therefore the Phantom Menace of the exoplanet world.

Credit: David A. Aguilar (CfA)

View Caption+#6: Keeping Warm

The habitable zone seems to be the pinnacle of extraterrestrial living. If you're an alien with similar needs to life on Earth, then you'll need liquid water. If your planet exists outside your star's habitable zone, well, you're in trouble. Either your world will be frozen like a block of ice, or boiling like a kettle. But say if your world had the ability to extend your star's habitable zone?
There may be some atmospheric factors that might keep water in a comfy liquid state. Even better, if you like deserts, a dry world could even be oddly beneficial.

Image: A cool world some distance from its st

View Caption+#7: Crazy Aurorae

Planets with a global magnetic field, like Earth, have some dazzling interactions with the winds emanating from their stars. The high-energy particles bombard the planet's atmosphere after being channeled by the magnetism. A wonderful auroral lightshow ensues.
But say if there's an exoplanet, with a magnetosphere, orbiting really close to its star? Well, stand back! The entire world would become engulfed in a dancing show, 100-1000 times brighter than anything we see on Earth.

Image: A "hot Jupiter" and its two hypothetic

View Caption+#8: The "Candidates"

"Candidate" exoplanets are often mentioned, especially when talking about detections by the Kepler space telescope. But what does this mean?
As a world passes in front of its star, slightly dimming the starlight, this isn't considered a "confirmed" exoplanet detection. To make sure that signal is real, more orbital passes of the exoplanet need to be logged before a bona fide discovery can be announced. Until then, these preliminary detections are called exoplanet candidates.

Credit: Adrian Mann, <a href="http://www.bisb

View Caption+#9: Angry Suns, Naked Planets

Exoplanets come in all sizes and all states of chaos. Some might have wonky orbits, others might be getting naked. Other times, they're simply being ripped apart by X-rays blasted from their parent star. Bummer.

Image: An exoplanet being destroyed by X-rays

View Caption+#10: Super-Earths

Super-Earths get a lot of press. Mainly because "Earth" is mentioned. Sadly, most of these worlds are likely completely different to anything we'd call "Earth." And you can forget calling the vast majority of them "Earth-like." It's simply a size thing -- they're bigger than Earth, yet a lot smaller than Jupiter, hence their name, "super-Earth." Easy.

Image: Artist's impression shows HD 85512b, a

View Caption+#11: Let's Go!

For now, we have to make do with artist's renditions of exoplanets for us to visualize how they may look in their alien star systems.
However, plans are afoot to send an unmanned probe to an interstellar destination. Although these plans may be several decades off, seeing close-up photographs of these truly alien worlds will be well worth the wait.

Credit: Adrian Mann, <a href="http://www.bisb

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By combining two cutting-edge astronomical techniques, researchers of the University of California, Berkeley, the SETI Institute and their international collaborators have been able to, for the first time, resolve the visible light of the two stars in the famous Capella binary system. Now it is hoped that the method will be used to seek out and directly image dim exoplanets that orbit bright stars.

Located some 43 light-years from Earth, Capella is the brightest “star” in the constellation Auriga. However, Capella is actually two stars but they orbit so close, approximately the distance of Venus’ orbital distance from the sun, that their combined light ensures they cannot be resolved individually.

This poses an interesting problem for astronomers. Often exoplanets, circumstellar dust and other stellar partners remain invisible, masked by the overwhelming brightness of the parent stars, but as this Capella test has confirmed, it is possible to resolve individual stellar objects in close proximity to one another.

Until now, the binary star system Capella appeared in visible light telescopes as a single ‘star’ larger than the red dotted circle. FIRST was able to resolve the two stars and, based on six individual observations at three different times over a 14 month time period, confirm the proposed elliptical orbit of one of these stars around its companion.

Gaspard Duchene/UC Berkeley and Franck Marchi/SETI Institute

Three years ago, the Fibered Imager foR Single Telescope (FIRST) prototype instrument was attached to the Shane 3-meter telescope at the University of California Lick Observatories in San Jose, Calif. Now, an upgraded version of FIRST has been installed at the powerful 8-meter Subaru telescope in Hawaii. It is hoped one day that the instrument will be able to resolve dim, Earth-sized worlds orbiting M-class dwarf stars — a type of star that is of increasing interest to exoplanet hunters.

“With the FIRST instrument at Subaru telescope, we expect to be able to resolve giant and super giant stars and observe the close environment of debris disks around young stars,” said SETI Institute astronomer Franck Marchis, co-author of the study to be published in the journal Astronomy and Astrophysics.

FIRST combines the power of interferometry with the resolving prowess of adaptive optics. Both Shane and Subaru telescopes are fitted with adaptive optics, a laser system that adapts the telescopes’ optics to counteract turbulence in the Earth’s atmosphere.

By using ultra-fine optical fibers feeding into the back of the telescopes’ mirrors at 18 different points, extreme contrast between light (star) and dim (potential exoplanets) objects can be attained. This form of interferometry allows the light being collected from different parts of the mirror to interfere with itself, creating high-resolution images. FIRST also collects spectroscopic data from its targets, giving astronomers information about stellar composition and, potentially, exoplanet atmosphere composition.

The power of the system is tremendous. Detail in binary star systems, protoplanetary dust, even surface features in bloated red giant stars can be attained, but the system will need some refinement before exoplanetes can be resolved.

Currently, the FIRST system can resolve objects that differ in brightness by 50-100 times. This is good, and can be used to easily distinguish between the stars in Capella. But in the case of exoplanets, where orbiting Jupiter-sized worlds are 10,000-100,000 times dimmer and Earth-size planets are a million times dimmer than their host stars, FIRST is woefully under powered.

“If we could add enough fibers, we could get very high contrast; that is the goal,” said lead researcher Gaspard Duchêne of UC Berkeley. “If we can scale this up to look for planets, it would be very, very exciting.”